Radiation regenerative burner

ABSTRACT

A method and device for increasing the overall efficiency of transfer of energy from a gas-fueled radiant burner to a load which contemplates the use of at least one reradiator and preheater for the fuel and air mixture.

United States Patent Solbrig Aug. 15, 1972 RADIATION REGENERATIVE BURNER [72] Inventor: Charles W. Solbrig, Idaho Falls,

Idaho [73] Assignee: Institute of Gas Technology [22] Filed: Oct. 19, 1970 [21] App1.No.: 81,998

[52] US. Cl ..263/l9 R, 165/6, 431/328 [51] Int. Cl ..F23d 13/12 [58] Field of Search.....165/6; 431/328; 263/19 R, 52

[56] References Cited UNITED STATES PATENTS 2,740,615 4/1956 Scholl ..165/6 3,384,358 5/1968 Morton ..165/6 FOREIGN PATENTS OR APPLICATIONS 1,263,387 5/1961 France ..43l/328 Primary Examiner-John J. Camby Att0rney-Molinare, Allegretti, Newitt & Witcoff ABSTRACT A method and device for increasing the overall efficiency of transfer of energy from a gas-fueled radiant burner to a load which contemplates the use of at least one reradiator and preheater for the fuel and air mixture.

16 Claims, 3 Drawing F igures RADIATION REGENERATIVE BURNER CROSS-REFERENCE TO RELATED APPLICATION Some of the terminology in this application is explained in detail in my co-pending application Ser. No. 82,109, filed Oct. 19, I970, for RADIANT GAS BURNER DEVICE FOR HEATING, the disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION The present invention relates to a novel radiant burner and, more particularly, it relates to a novel radiant burner having increased overall efficiency of transfer of energy from a gas-fueled radiant burner to a load.

Gas-fueled radiant burners are known in the art. See, e.g., Schwank US. Pat. No. 2,775,294. When the terms radiation burners or radiant burners are used herein, it is meant a gas-fueled burner. Such radiation burners possess advantages over other devices: they consume a gaseous fuel which is both a cleaner and a less expensive form of energy than electricity; they can also be more positively controlled than comparable electrical devices. Therefore, there is a need for gasfueled radiation burners having improved overall efficiencies.

It is, accordingly, an object of the present invention to provide a novel gas-fueled radiation burner.

It is another object of the present invention to provide a gas-fueled radiation burner having substantial increased overall efficiency.

These and other objects of the invention can be gathered from a reading of the following disclosure.

SUMMARY OF THE INVENTION In accordance with the present invention, a novel radiation burner is provided which has increased overall efficiency of transferring energy from a gaspowered radiant burner to a load by the use of a regenerative radiator. The regenerative radiator is used both as a preheater and as a reradiator.

BRIEF DESCRIPTION OF THE DRAWING AND DESCRIPTION OF THE PREFERRED EMBODIMENT As indicated above, the novel gas-fueled radiant burner of the present invention yields increased overall efficiencies by the use of a regenerative radiator which is used both as a preheater and as a reradiator. In order for the regenerative radiator to act both as a reradiator and as a preheater for the fuel and air mixture, a portion of the regenerative radiator is disposed between a principal radiator and the load or exterior of the burner device, while another portion of the regenerative radiator is positioned between the fuel and air inlet in the burner block (housing) and the principal radiator.

In practice, the objects of the invention can be achieved by passing a fuel and air mixture into a burner device wherein the mixture is burned near the surface of a principal radiator. The principal radiator may be made of any of the known materials for this purpose. The material employed for the principal radiator should, however, be a good coupler with the load to be heated. That is to say, the principal radiator should emit most of its radiation in the wavelength region which is easily absorbable by the load to be heated. For most conventional purposes, such as a heater for warming people in a room, materials such as ceramic tile and zinc oxide are suitable for use as the principal radiator. I prefer to make the principal radiator from a percent solid area zinc oxide which is porous to gases. In this manner, the fuel and air mixture can pass through the zinc oxide radiator and be burned on or near the far side of the radiator.

The invention will now be further described in connection with the drawings, in which:

FIG. I is a schematic view showing a radiant burner in accordance with the invention, having a rotary reradiator in the form of a cylinder or sphere;

FIG. 2 is a schematic view of a radiant burner embodying the present invention having a reradiator in the form of an endless belt which is made from small flat plates or wires flexibly joined together; and

FIG. 3 is another schematic view showing a further embodiment of the present invention in which the reradiator is stationary but thermally connected to a preheating element.

Referring to FIG. 1, a radiant burner is generally shown at 10. Burner 10 has a housing 11 which may be cylindrical or spherical in shape, depending on the shape of the radiator employed therein. In the present embodiment, the housing 11 and radiators are either of cylindrical or spherical shape. A stationary principal radiator 12, in the form of a half cylinder or hemisphere is located in the front of the radiant burner 10. A rotatably mounted cylindrical or spherical secondary radiator or reradiator 13 is disposed so that reradiator 13 substantially envelopes the principal stationary radiator 12. The mixture of fuel and air 15 enters the radiant burner via a conduit 16 and passes through the rear portions of the cylindrical or spherical and rotary reradiator 13. The fuel and air mixture then proceeds to contact the stationary principal radiator 12 which is porous and combustion takes place on the exterior surface of principal radiator 12, in the space 60 between the radiators l2 and 13. The combustion products pass through reradiator l3 and out of the radiant burner to the surroundings. As the secondary radiator or reradiator 13 is rotated around its axis 14, a portion of the reradiator is first heated by the combustion products and the heated portion is then rotated (in a clockwise direction in this particular embodiment) to the rear of the radiant burner 10 to contact the fuel and air mixture 15.

In this manner, the reradiator 13 serves two functions: first, it serves as a reradiator in the position in front of the principal radiator 12; and secondly, it serves as a preheater to preheat the fuel and air mixture prior to the latters contact with the principal radiator. A seal 17 connects the housing 11 and the principal radiator 12 so that the fuel and air mixture must pass through the principal radiator and be burned thereat. The combustion products then pass through the reradiator into the surroundings and are exhausted by, for example, exhaust means disposed in any convenient place. For example, where the burner of this invention is disposed in an appliance cavity, the usual exhaust ports may be provided. Alternatively, for an exposed burner, a suction fan and opening may be disposed adjacent the burner so that the exhaust products are swept away. In many cases exhaust means will not be necessary since complete combustion to CO and H are obtained.

The radiant burner shown in FIG. 1 may have its housing made of a solar absorber material. One such material is described in Schmidt, R. N. and Jansen, J .E., Selective Coatings for Vacuum-Stable, High Temperature Solar Absorbers, Paper No. 49, Symposium on Thermal Radiation of Solids, NASA SP55, P508-24, Washington, D. C., National Aeronautics and Space Administration, 1965. One such solar absorber material is made of molybdenum with three interference coatings of alumina, molybdenum and alumina. The secondary or reradiator may also be made of this solar absorber material, except that the reradiator should have about percent solid area. A much greater or a much smaller area in the radiator 20 percent) would result in a decreased efficiency.

FIG. 2 shows another embodiment of the rotary type of reradiator shown in FIG. 1. In FIG. 2, a radiant burner 22 is shown having a housing 23 connected at one end with a fuel and air inlet 24 and at the other end with a seal 25. Within housing 23, there is disposed a flow diffuser 26 for distributing the fuel and air admitted into the burner. The seal is connected to a pair of rollers 27 around which a reradiator 28 is rotated. Reradiator 28 may be made, for example, of two metal bands 29, one disposed at each end of the rollers. These bands are connected by wires 30 which are made of the desired reradiator material. Altematively a belt of flat plates flexibly joined together along adjacent edges may be used. Reradiator 28 is rotated by rollers 27 which are driven by conventional means (not shown). Between the front side of reradiator 28 and the back half of the same, there is positioned a principal radiator 31 with seals 61 and 62 at each end. When in operation, the fuel and air mixture is admitted into burner 22 and distributed by the flow diffuser 26 which is considered part of the burner housing. The mixture then contacts the back half of the rotary reradiator to be preheated thereby. The preheated fuel and air mixture then passes through the porous principal radiator 31 and burns very close to the surface of the principal radiator 31. The combustion products then pass through reradiator 28 and are exhausted from the burner 22 thereafter.

Instead of a rotary reradiator, the regenerative radiator of the present invention may be made as shown in FIG. 3. In FIG. 3, a radiant burner 32 is shown having a housing 33 with a fuel and air inlet 34. A stationary reradiator 35 is located in front of radiant burner 32. Stationary reradiator 35 is connected through heat conductor elements 36 to a preheating, heat transfer element 37. Between reradiator 35 and preheating element 37, there is mounted the principal radiator 38. Principal radiator 38 is attached through insulating supports 39 to elements 36. The elements 36, in turn, are attached through insulating support 40 to housing 33. In this embodiment, the fuel and air mixture is first preheated by element 37 and then passes through principal radiator 38 to be burned near the surface of radiator 38 between reradiator 35 and principal radiator 38. The combusted products then pass through reradiator 35 and are exhausted from the burner 32. Heat is conducted from reradiator 35 via conductors 36 to preheating element 37. More than two conductors may be used if they are suitably insulated from the principal radiator and if they do not interfere appreciably with the radiation.

For the embodiments using a plurality of reradiators and gas-air preheating heat transfer elements, it is preferred that the reradiator closest to the principal radiator is thermally connected to the preheater heat transfer element closest to the principal radiator. The second closest reradiator is connected to the second closest preheater, and so on. This ensures the best input and output temperature gradient. The reradiators may be movable as in FIGS. 1 and 2 or, preferably are fixed with the principal radiator being thermally connected by a heat conductor element to the appropriate heat transfer element.

The use of a regenerative radiator with a reradiator portion and a preheater portion, as can be seen from the efficiencies in Table I, increases the overall efficiency of a radiant burner. The principal radiator in Table I is made of opaque zinc oxide with percent solid area but porous to gases. The housing and the reradiator are made of the solar absorber material such as the interference coated molybdenum described above, with the reradiator having a 20 percent solid area. As a load, a thin film of water is used. A thin water film is a common material to be heated since many processes involve drying and is also representative of many other load materials.

The efficiencies were determined,in part by calculation using radiation heat transfer principles and reported radiation data of materials, and are presented below in Table I.

TABLE I Radiation Regenerator Principal Radiator coupling Rated Effic- Efficiency 1 iency 1 A. Opaque ZnO B. Opaque ZnO C. Opaque ZnO D. Opaque ZnO E. Opaque ZnO F. Opaque ZnO In the above table, the definitions for the various efiiciencies are:

m Coupling Efficiency Radiant heat absorbed by the work Radiant heat emitted by the heater m Rated Efficiency Radiant heat emitted by the heater 1 Overall Efficiency 1;, X 1;,

: Radiant heat absorbed by the work X Total heat supplied to the heater 1 For further detailed description of these terms, reference is made to my co-pending application Ser. No. 82,109, filed Oct. 19, 1970, for RADIANT GAS BURNER DEVICE FOR HEATING. I

As can be seen from Table I, when the burner has only the principal radiator therein, an overall efficiency of about 15.73 percent is achieved. When a reradiator is disposed in front of the principal radiator without a preheating means, the overall efficiency drops to 14.71 percent. This particular reradiator (using solar absorber material) does not couple well with the thin film of water which results in a drop in the coupling efficiency. In turn that causes the drop in overall efficiency. Table I then shows four examples where the use of a reradiator is coupled with a preheating element: with the effective heat transfer coefficient, h, between the reradiator and preheating section being varied between 2 and 160 Btu/hr-ft F. With the preheating element, the overall efficiency of the radiant burner increases from 15.18 to 19.89 percent, depending on the heat transfer coefficient between the reradiator and the preheating element. Thus, by the use of a regenerative radiator having a reradiation section and a preheater section, the overall efficiency of a radiant burner can be increased by more than percent.

Table 11 below shows use of a different material which is a good coupling material with a thin film of water'as the regenerative radiator. In Table II, the regenerative radiator is made of oxidized Inconel having 20 percent solid area.

Present day radiant burner efficiencies are generally represented by the efficiencies for oxidized Inconel shown above as H in Table II. It is seen that the Inconel radiator is less efficient than the zinc oxide radiator alone, although the rated efficiency for the Inconel radiator is higher than that for the zinc oxide radiator.

However, when a combination of zinc oxide principal radiator and Inconel reradiator is employed, 1 in Table 11 above, the overall efficiency is substantially increased. This is due to the relatively high coupling efficiency of the Inconel for the thin film of water to be heated, as compared to the solar absorber reradiator shown in Table I. Finally, when a radiant burner having a zinc oxide principal radiator, an Inconel reradiator and a preheating element connected to the reradiator with a heat transfer coefficient thereinbetween of 160 Btu/hr-ft F, J in Table 11 above, the overall efficiency is greatly increased thereby.

Comparing the figures in Table 11 above, it can be seen that by the use of a radiation regenerator with a heat transfer coefficient of about 160, the overall efficiency is increased to 20.21 percent. The corresponding overall efficiency for an oxidized Inconel reradiator system is 17.52 percent. Comparing these figures with a simple zinc oxide radiator, which has an overall efficiency of 15.73 percent, it is seen that the increase in efficiency by the use of the regenerative concept is about 2.5 times the increase in efficiency obtainable by the use of a simple reradiator.

The overall efficiencies for both regenerative burners shown in Tables I and 11 with h 160 is seen to be comparable. While I do not wish to be bound by theory, it appears that since one is a poor coupling material with a thin film of water, while the other is a good coupling material, the increased efficiency is due to the use of the regenerator. This permits the least expensive material to be used for the regenerator radiator. Indeed it is found that by using the regenerator of this invention the increase in the overall efficiency is usually accompanied by a decrease in the coupling efficiency and an increase in the rated efficiency.

Table III below shows the efficiencies for two other regenerative radiator systems. The first uses a different material for the preheater than for the reradiator. The second illustrates the benefit which can be obtained with a double regenerator.

TABLE III OTHER RADIANT BURNERS WITH AN INPUT FLOW RATE OF 2000 SCFH/ft K Four-Radiator System 1. Burner block solar absorber solid area 2. Preradiator solar absorber 20% solid area 3. Principal radiator zinc oxide 100% solid area 4. Reradiator chromium oxide 20% solid area h Between (2) and (4) is Btu/hr-ft -F L. Six-Radiator System 1. Burner block solar absorber 100% solid area 2. First preradiator solar absorber 20% solid area 3. Second preradiator solar absorber 20% solid area 4. Principal radiator zinc oxide 100% solid area 5. First reradiator chromium oxide 20% solid area 6. Second reradiator chromium oxide solid area h Between (2 and (6) is 160 Btu/hr-ft F h Between (3) and (5) is 160 Btu/hr-ft -F The presently preferred system of those shown in Table III above comprises a zinc oxide principal radiator, two chromium oxide reradiators and two solar absorber material preheating elements. For such a regenerative radiator system, the overall efficiency is 23.89 percent. When this figure is compared to the 13.52 percent for the present day radiator systems, there is an increase in the overall efficiency of about 77 percent. It should be noted that the efficiencies representative of present day gas fired radiant burners mentioned above were determined by using the radiation properties of lnconel even though present day burners are usually made of some type of oxide, including in that category, ceramic material. However, the impurities used in the ceramic burner increase the emittance of the resulting burner so that the radiation properties are effectively the same as lnconel.

The invention has been described in detail with reference to particular and preferred embodiments thereof, butit will be understood that variations and modifications can be made within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What is claimed is:

1. A method for production and transfer of radiant energy resulting from the combustion of fuel to a load which comprises:

a. passing a fuel and air mixture to a principal energy radiator, combusting said fuel and air mixture at said principal radiator to produce radiant energy and combustion products,

c. passing said combustion products to a second radiator disposed in association with said principal radiator and said load,

.- transferring heat from said second radiator to said fuel'and air mixture prior to combustion at said principal radiator, so that said second radiator both preheats said incoming fuel and air mixture and reradiates energy to a load disposed in energy receiving relation thereto.

2. A method as in claim 1 wherein said fuel is natural gas. I

3. A method as in claim 1 wherein said second radiator is in a form enveloping said principal radiator, and which includes the step of moving said second radiator so that a portion of the said radiator is first contacted with the combustion products at a point between said principal radiator and said load, and said portion is then moved to be in heat transfer relation to said fuel and air mixture before said mixture comes into contact with said principal radiator.

4. A method as in claim 1 wherein said second radiator is stationary, and said heat is transferred from said reradiator by a heat conductor to said fuel and air mixture and is preheated thereby.

5. An apparatus for efficiently transferring energy resulting from the combustion of fuel to a load which comprises: a housing having an inlet opening and exit opening; a principal radiator located in said housing;

means for passing said fuel and air into said housing through said inlet opening to be combusted at said principal radiator; a reradiator located in said housing between said principal radiator and said exit opening so that the combustion products from said principal radiator will pass said reradiator prior to leaving said housing; means for transferring heat from said reradiator to said fuel and air mixture prior to the latters contact with said principal radiator.

6. An apparatus according to claim 5 further com prising means for exhausting said combustion products located between said reradiator and said exit opening.

7. An apparatus as in claim 5 wherein said reradiator comprises a rotatably mounted cylinder, and said heat transferring means comprises means for rotating said reradiator around its axis, to first pass a portion of said reradiator between said principal radiator and said exit opening to be heated by the combustion products and then pass said portion between said inlet opening and said principal radiator to preheat said fuel and air mixture prior to combustion of the latter.

8. An apparatus as in claim 5 wherein said reradiator comprises a rotatably mounted sphere, and said heat transferring means comprises means for rotating said reradiator around its axis, to first pass a portion of said reradiator between said principal radiator and said exit opening to be heated by the combustion products and then pass said portion between said inlet opening and said principal radiator to preheat said fuel and air mixture prior to combustion of the latter.

9. An apparatus as in claim 5 wherein said reradiator comprises a rotatably mounted'endless belt, and said heat transferring means comprises means for rotating said belt, to first pass a portion of said reradiator between said principal radiator and said exit opening to be heated by the combustion products and then pass said portion between said inlet opening and said principal radiator to preheat said fuel and air mixture prior to combustion of the latter.

10. An apparatus as in claim 5 wherein said reradiator is stationary, said heat transferring means comprises: l a gases preheating heat transferring element, located between said inlet opening and said principal radiator, and (2) a heat conductor connecting said preheater element to said reradiator to transfer heat from the combustion products to said reradiator and thence to said element and to the fuel and air mixture.

11. An apparatus as in claim 5 wherein said principal radiator is made of porous zinc oxide and said reradiator is made of a solar absorber material.

12. An apparatus as in claim 5 which includes a-plurality of reradiators, each of which is connected to a heat transferring element for preheating said fuel and air mixture.

13. An apparatus as in claim 10 wherein said heat transferring means includes a plurality of heat transferring elements, and which includes a plurality of reradiators, each of said reradiators is connected to a separate one of said heat transferring elements, the reradiator disposed adjacent the principal radiator is thermally connected to the preheater element adjacent the principal radiator.

14. An apparatus as in claim 13 wherein said principal radiator comprises a zinc oxide body porous to gases passage having about percent solid area, and

gases passage having about percent solid area, said m principal radiator is a zinc oxide material porous to gases passage having about percent solid area, and said reradiator is a chromium oxide material porous to gases passage having about 20 percent solid area 16. An apparatus as in claim 10 wherein the coefficient of heat transfer from said reradiator to said heat transferring element is on the order of Btu/hr-ft F. 

1. A method for production and transfer of radiant energy resulting from the combustion of fuel to a load which comprises: a. passing a fuel and air mixture to a principal energy radiator, b. combusting said fuel and air mixture at said principal radiator to produce radiant energy and combustion products, c. passing said combustion products to a second radiator disposed in association with said principal radiator and said load, d. transferring heat from said second radiator to said fuel and air mixture prior to combustion at said principal radiator, so that said second radiator both preheats said incoming fuel and air mixture and reradiates energy to a load disposed in energy receiving relation thereto.
 2. A method as in claim 1 wherein said fuel is natural gas.
 3. A method as in claim 1 wherein said second radiator is in a form enveloping said principal radiator, and which includes the step of moving said second radiator so that a portion of the said radiator is first contacted with the combustion products at a point between said principal radiator and said load, and said portion is then moved to be in heat transfer relation to said fuel and air mixture before said mixture comes into contact with said principal radiator.
 4. A method as in claim 1 wherein said second radiator is stationary, and said heat is transferred from said reradiator by a heat conductor to said fuel and air mixture and is preheated thereby.
 5. An apparatus for efficiently transferring energy resulting from the combustion of fuel to a load which comprises: a housing having an inlet opening and exit opening; a principal radiator located in said housing; means for passing said fuel and air into said housing through said inlet opening to be combusted at said principal radiator; a reradiator located in said housing between said principal radiator and said exit opening so that the combustion products from said principal radiator will pass said reradiator prior to leaving said housing; means for transferring heat from said reradiator to said fuel and air mixture prior to the latter''s contact with said principal radiator.
 6. An apparatus according to claim 5 further comprising means for exhausting said combustion products located between said reradiator and said exit opening.
 7. An apparatus as in claim 5 wherein said rerAdiator comprises a rotatably mounted cylinder, and said heat transferring means comprises means for rotating said reradiator around its axis, to first pass a portion of said reradiator between said principal radiator and said exit opening to be heated by the combustion products and then pass said portion between said inlet opening and said principal radiator to preheat said fuel and air mixture prior to combustion of the latter.
 8. An apparatus as in claim 5 wherein said reradiator comprises a rotatably mounted sphere, and said heat transferring means comprises means for rotating said reradiator around its axis, to first pass a portion of said reradiator between said principal radiator and said exit opening to be heated by the combustion products and then pass said portion between said inlet opening and said principal radiator to preheat said fuel and air mixture prior to combustion of the latter.
 9. An apparatus as in claim 5 wherein said reradiator comprises a rotatably mounted endless belt, and said heat transferring means comprises means for rotating said belt, to first pass a portion of said reradiator between said principal radiator and said exit opening to be heated by the combustion products and then pass said portion between said inlet opening and said principal radiator to preheat said fuel and air mixture prior to combustion of the latter.
 10. An apparatus as in claim 5 wherein said reradiator is stationary, said heat transferring means comprises: (1) a gases preheating heat transferring element, located between said inlet opening and said principal radiator, and (2) a heat conductor connecting said preheater element to said reradiator to transfer heat from the combustion products to said reradiator and thence to said element and to the fuel and air mixture.
 11. An apparatus as in claim 5 wherein said principal radiator is made of porous zinc oxide and said reradiator is made of a solar absorber material.
 12. An apparatus as in claim 5 which includes a plurality of reradiators, each of which is connected to a heat transferring element for preheating said fuel and air mixture.
 13. An apparatus as in claim 10 wherein said heat transferring means includes a plurality of heat transferring elements, and which includes a plurality of reradiators, each of said reradiators is connected to a separate one of said heat transferring elements, the reradiator disposed adjacent the principal radiator is thermally connected to the preheater element adjacent the principal radiator.
 14. An apparatus as in claim 13 wherein said principal radiator comprises a zinc oxide body porous to gases passage having about 100 percent solid area, and which includes two reradiators comprising chromium oxide bodies of about 20 percent solid area, and two preheating heat transfer elements comprising solar absorber material having about 20 percent solid area.
 15. An apparatus as in claim 10 wherein said housing includes a burner block porous to gases passage of solar absorber material having about 100 percent solid area, said preheator is a solar absorber material porous to gases passage having about 20 percent solid area, said principal radiator is a zinc oxide material porous to gases passage having about 100 percent solid area, and said reradiator is a chromium oxide material porous to gases passage having about 20 percent solid area.
 16. An apparatus as in claim 10 wherein the coefficient of heat transfer from said reradiator to said heat transferring element is on the order of 160 Btu/hr-ft2-* F. 